Patent GB-486764-A (GB)
Title: Improvements in or relating to electrical communication systems
IPC: H04Q1/36
Filed: 1936-12-03
Abstract: 486,764. Automatic exchange systems. ELLIS, H. O., and COOPER, W. H. B. Dec. 3, 1936, Nos. 33169/36 and 3032/37. [Class 40 (iv)] [Also in Group XL] In a forward - loop impulsing system for telephone or telegraph exchanges, impulses are generated at an outgoing repeater by means of normally closed relay or interrupter-contacts bridged across the line which has connections to batterv and earth during the sending period. Preferably a network is provided to make the growth and decay curves of the impulses symmetrical. Two systems are described. Transmission of impulses. When the operator plugs into the circuit shown in Fig. 3, relays S, SS, L are operated and a flicker signal is given. When the dialling key is thrown, RR is operated temporarily and DT locks and connects up impulse relay A, which is followed by B, and afterwards repeats the digits to magnet RM of a mechanical regenerator in parallel with a sluggish relay C. The latter energizes IP, IS and magnet MM, which opens springs Mdm. Springs NS are closed when there is relative displacement between the sending and receiving parts of the regenerator. At the end of the first digit C. and MM are released and BY is energized and locks up over springs NS, energizing N, DE. This makes a new bridge across the outgoing junction in which Z pulls up energizing CX which breaks the bridge to prepare the incoming end and causes IP, IS to fall sluggishly in succession. A circuit is then made for magnet SM which starts the transmission of the first digit. On the operation of SM, springs Sdm open, DE, CX fall back and IP, IS reoperate, releasing SM. The junction is now bridged by the impulse springs IMPS via an impedance network designed to give a symmetrical form to the impulses and to suppress the higher frequencies, and matched to the impedance of the line by means of resistance RO3 and condenser CC1. At the same time, battery and ground are connected to the impulse springs and accordingly an impulse goes forward each time they open. Each digit sent out is terminated by the engagement at PP of the re-set pin carried by the sending arm of the regenerator with the displaced pin and the consequent reoperation of DE. The re-connection of AA, X at the receiving end, Fig. 4, as described below energizes Z, and CX then initiates the transmission of a new digit by releasing IP, IS which time the interdigital pause. After the final digit however, springs NS are opened and BY falls followed by IP, IS and N and, when AA, X are reconnected to the junction at the incoming end, IL pulls up. Restoration of the dialling key energizes LR and releases DT and A, and the operation of IL thus causes the lamp connected to the sleeve circuit to glow continuously. Reception of impulses. The preliminary looping of the outgoing end of the junction energizes AA, X, BA, Fig. 4. The latter bridges the wires L5, L6 through relay I which pulls up in series with the feed ahead. When the loop on L3, L4 is broken by the operation of CX, the relapse of X energizes XY which energizes YA and transfers the junction to the forward loop comprising matching impedances RC1, RR1, a network LL1, LL2, RR1, RR2 designed to suppress frequencies above 120 cycles, and the primary of a transformer T which is of low inductance to avoid distortion of the incoming impulses. The secondary is connected to a pentode amplifier V having an adjustable self-bias resistance R5 which regulates the normal current through the winding e of a repeating relay P and also provides negative retroaction. This relay has also a winding f acting in opposition to winding e and connected up shortly after the circuit is seized, to give time for surges in the line to die down, and holding windings g, h controlled by a high-speed relay HSB. At the beginning of each impulse, the flux through e is momentarily reduced and the contact changes over and is held in the changed position by its winding h. At the end of the impulse, the flux through e is momentarily increased and the contact is restored and held in the restored position by winding g. An additional quick acting relay HS repeats the impulses over the circuit L5, L6. The shape of the repeated impulses is governed by resistances H, W arid condenser HH. YA improves the out-impulsing circuit and energizes BB. CR is operated during each digit and energizes BC, RD. At the end of the digit, CR, YA, XY fall back and AA, X are thus reconnected to the junction. If relay N is still energized, Z, Fig. 3, is now energized over the junction, and energizes CX to initiate the transmission of a new digit and to cause the relapse of X and consequent energization of XY to reconnect the receiving apparatus. After the final digit however, since N, Fig. 3, is released, AA, X remain energized in series with IL, Fig. 3 and XY is not again energized. Repetition of busy signal. Busy flash received over L5, L6 is repeated by I which on its first relapse releases BB so that its next operation energizes BR. BR locks and subsequent flash impulses are repeated by I over X and L4. Modified system, Figs. 1 and 2 (not shown). This system resembles that described above but a signal in the form of a current reversal is sent to inform the incoming end that no more digits are to be sent.